A possible way to avoid jitter issues in a DAC box fed by a SPDIF from a CD transport: build a large enough buffer that can hold enough bits to buffer the total timing error between the clock in the DAC and the clock in the CD transport, both free running. Quartz crystals are usually about 0.005 % accurate, so the free running error between two such clocks over 75 minutes (the max length of a CD) would be about half a second (worst case if one clock is high and the other low). A 1 megabit memory chip would support this. The DAC box would have a receiving chip with a PLL to receive the incoming bits from the transport. Then these bits would feed into a dual port memory clocked in off the PLL clock, and then in turn clocked out of this dual ported memory using an independent free running low jitter clock and then fed to the DAC chips. There would be a delay of the music of about half of the size of the memory (about 3/4 second) when a CD begins, and as the CD plays either the transport or the DAC eventually fills or emptys the FIFO memory, but this shouldn't happen before the CD is over.
Anyone do something like this?
Anyone do something like this?
In Poland we say: don't fight a fly with a cannon.
I don't think you need sophisticated quartz clock. I'd rather use cascade of PLLs with gradually decreasing border frequency of loop lowpass filter. This way you will get equal mean frequencies of input and output with great jitter cancellation and reasonable size of fifo memory.
regards
I don't think you need sophisticated quartz clock. I'd rather use cascade of PLLs with gradually decreasing border frequency of loop lowpass filter. This way you will get equal mean frequencies of input and output with great jitter cancellation and reasonable size of fifo memory.
regards
darkfenriz said:
Perhaps if you did...., well thats another story for another place.
The clock at the dac end of a FIFO is as simple at it gets, a lot simple than multiple PLLs. The other advantage of a FIFO is that it fixes one end of the chain rather than having a continuous search for equilibrium, a process, the Sith Lord for one, reckons he can hear.
rfbrw said:
Maybe, but some of us are inputting a continuous digital input stream from mediaplayers, DVD in stead of the maximum 74 minutes of a cd
The buffer will either fill up or empty completely.And what about DVD synchronisation between sound and picture
I would love to find a custom PLL with small FIFO with 0-5V output for VCO that internally operates with variable gain;
if the error is high, the output signal to the VCO changes quickly, if the error is small, the output signal will change slowly.
So you operate sub 1Hz, but still have fast locking
rbroer said:
Maybe, but some of us are inputting a continuous digital input stream from mediaplayers, DVD in stead of the maximum 74 minutes of a cd
And what about DVD synchronisation between sound and picture
These are all valid concerns and, ideally, they would be addressed by faster-than-realtime data transfer.
I would not be surprised to find something like that already exists.
Not really a simple DIY building block for a digital secundary PLL, but it seems http://www.lavryengineering.com uses a technique in their DA's called CrystalLock.
Seems just what I want, short FIFO, but still low corner frequency.
Just wonder how they manage the 3 standard sampling frequencies ?
Switching between 3 pullable crystals ?
Seems just what I want, short FIFO, but still low corner frequency.
Just wonder how they manage the 3 standard sampling frequencies ?
Switching between 3 pullable crystals ?
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